The present invention relates to the technology of reconnecting the connection in failures of a line/failures of an apparatus in an ATM switched network, particularly in an ATM swiched network in which terminals are connected through software PVCs.
A P-NNI (Privatexe2x80x94Network Node Interface) is one of service interfaces of an ATM (Asynchronous Transfer Mode) switched network, and is the convention for connecting between the public networks and the private networks in order to switch the address information or the routing information.
In the P-NNI, it is possible to establish a software PVC (software Permanent Virtual Connection: hereinafter, referred to as xe2x80x9can SPVCxe2x80x9d or xe2x80x9ca software PVCxe2x80x9d for short, when applicable). In this case, the PVC is established only between a UNI (User Network Information) of a source and the UNI of a destination, and ATM nodes (ATM switching equipment) which are arranged in the middle of the UNI of the source and the UNI of the destination are connected through an SVC (Switched Virtual connection). As a result, it is said that the P-NNI is the technology which is capable of realizing the dynamic routing between the ATM switching equipment.
Now, the description will hereinafter be given with respect to the system configuration of the ATM network with reference to FIG. 1.
In the figure, a terminal 101a (#A) and ATM switching equipment 102, and ATM switching equipment 104 and a terminal 101b (#b) are respectively connected through PVCs (Permanent Virtual Connections), and interchange routes (between ATM switching equipment) are connected through the SVCs.
Now, when the SPVC is set in the ATM switching equipment 102, for the SVC part of the interchange routes, the ATM switching equipment 102, 103 and 104 automatically sets the connections to maintain the connections. The features of this system are the following two points.
Since the ATM switching network has the SVCs set therein, if a VC (Virtual Connection) is, in occurrence of the failures, released due to the failures or the like (e.g., occurs between the ATM switching equipment 103 and 104), then the ATM switching equipment 102 on the transmission side recalls the ATM switching equipment 104 on the reception side, thereby ensuring the alternate route (the ATM switching equipment 102xe2x86x92105xe2x86x92104).
By only setting the terminal information of the both of the terminals (an ATM address of the terminal 101a (#A), VPI/VCI=a, an ATM address of the terminal 101b (#b), and VPI/VCI=b) and the like in both of the ATM switching equipment 102 on the transmission side and the ATM switching equipment 104 on the reception side, the PVC over the overall of the ATM network can be set.
FIG. 2 shows a hierarchy structure in the ATM. In occurrence of the failures in the above-mentioned paragraph (1), the alternate route is determined in the ATM layer shown in FIG. 2.
FIG. 3 shows the procedure of this failure recovery in the form of a flow chart.
When the failures occur in the location between the switching equipment 103 and 104 as shown in FIG. 1 (Step 301), in order that the processing may proceed to the alternate operation in the ATM switching network, the following processings are required.
First of all, the VC (Virtual Connection) needs to be disconnected in the ATM switching network (Step 302).
In this connection, in the data link monitoring timer installed in each of the ATM switching equipment, it takes normally about 17 seconds to disconnect the VC. This numeric value is obtained by summing 7 seconds defined for Timer No Response and 10 seconds of a L3 timer T309.
If the contents of a routing table are updated in recalling made from the terminal 101a (#A)(an Owner switching equipment in the case of the SPVC, but in this case, the ATM switching equipment 102), the alternate route is ensured.
Now, in order to make a recall, it becomes the prerequisite that any of the prior calls is already released. The data link monitoring timer for confirming the disconnection of the VC is arranged in the ATM layer in the hierarchy structure shown in FIG. 2.
Secondly, it is required that the contents of the routing table are already updated (Step 303).
Now, the numeric value which is obtained by multiplying xe2x80x9cHello packet sending time intervalxe2x80x9d by xe2x80x9cthe number of Hello packet sendingsxe2x80x9d becomes the update time of the routing table. Then, if the interval value is 15 secondsxc3x975 times, then the update time is 75 seconds in total.
This results from the function wherein xe2x80x9cIt is defined that the Hello packets are transmitted at intervals of 15 seconds from the adjacent node. If the Hello packet has not arrived,though the time period for the five times has elapsed for which the corresponding Hello packet is expected to essentially arrive, then the ATM switching equipment judges that the route to the adjacent node can not be used to update the contents of the routing table.xe2x80x9d
The reception sequence of the Hello packet between the nodes in occurrence of the failures in the prior art is shown in the form of a diagram in FIG. 6.
The route changing processing is only started when both of the steps 302 and 303 as described above have been confirmed (Step 305).
By the way, as apparent from the above-mentioned description, the time period required to update the contents of the routing table in the ATM switching equipment must be made longer than the time period required to disconnect the VC.
Now, in order that the alternate route may be set as speedily as possible, the time period required to update the contents of the routing table has only to be made slightly longer than the time period required to disconnect the VC.
The example associated therewith will be shown as follows.
Time intervals of sending Hello packets=15 seconds (setable range is a to b seconds).
The number of Hello packet sendings=2 times (setable range is c to d times).
If the values as described above are adopted, then the contents of the routing table are updated with the following conditions.
Minimum: 15 secondsxc3x972 times=30 seconds
Maximum: 14 seconds+15 secondsxc3x972 times=44 seconds
(The maximum time period required for the case where the failures occur on the line right after the Hello packet has been received from the adjacent node).
Now, with respect to the reconnection of the alternative connection in failures due to the SPVC, when making a detour to avoid the failure route, even if the route is restored from the failures to its former state, the terminal 101a (#A) and the ATM switching equipment 102 are connected to each other through the PVC, and hence no recall is made from the terminal 101a (#A). Therefore, since the ATM switching equipment 102 continues to maintain the SVC connection, no return of the state is made automatically back to the original route (the route in which the failures are recovered: the ATM switching equipment 102xe2x86x92103xe2x86x92104).
For this reason, there arises the problem that the connections for which the alternate route is selected are concentrated on some intervals and hence the network performance is continued to be pressed to induce the overcrowding.
In order to use the original route which has been restored from the failures to its former state, the definition in the table needs to be once released to carry out the registration again.
In this connection, there is known an OAM (Operation Administration and Maintenance) cell for reporting the failures between the nodes (between the ATM switching equipment) within the ATM network. As shown in FIG. 4, however, while after having recognized the node failures (Step 401), the failure report is made every connection (Step 402), the OAM cell has only the function of reporting in which direction the failures have occurred in the connection and hence does not contain therein the information which is used to specify the failure location at all.
For this reason, the node only receives the OAM cell and hence does not utilize the OAM cell for any of the operations at all (Step 403). In addition, while the received OAM cell may be utilized for the traffic control such as the overcrowding control in some cases (Step 404), it can not be utilized for the route control.
In the light of the foregoing, the present invention was made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide the technology which is capable of realizing the reconnection of an SVC (a software PVC) in failures on a line/failures in an apparatus for a very short time period.
According to first solving means of the present invention, in an ATM network in which a software PVC which is realized by a P-NNI, i.e., a PVC is established between a source private network and a destination private network, and the dynamic routing is carried out between ATM switching equipment on the basis of the establishment of an SVC, the ATM switching equipment is provided with failure detecting means for detecting occurrence of failures on a line.
Then, on the basis of the failures which have been detected in the physical layer, a failure information reporting cell is produced which contains therein the information used to specify at least the source ATM switching equipment and the ATM switching equipment for which the failures have occurred to report the occurrence of the failures of each of the ATM switching equipment. Then, the ATM switching equipment as the transmission side node reestablishes, in response to the above-mentioned failure information reporting cell, the alternate SVC which is set in such a way as to avoid the failure location.
In such a way, the detection of the failures is carried out in the ATM physical layer, which makes possible the rapid recover processing.
According to second solving means, in the above-mentioned first solving means, the recover of the failures which occurred on the line is detected in the physical layer of the ATM in a similar manner to that described above.
In such a way, the recovery reporting cell is reported to the ATM switching equipment as the transmission side node on the basis of the recover information which has been detected in the physical layer, whereby the SVC can be speedily established through the recover route. In this connection, at this time, the recovered SVC in the route in which the failures have been recovered is established while maintaining the alternate SVC which is set in such a way as to avoid the above-mentioned failure location, whereby the migration from the alternate SVC to the recover SVC becomes possible without interrupting the connection state through the SVC within the ATM network.
According to third solving means, in the above-mentioned first solving means, there is provided a management table in which the correspondence relation among the information which is used to specify the above-mentioned two terminals, the actual SVC which is established between the ATM switching equipment in the two terminals, and the stand-by SVC which is used in occurrence of failures.
As a result, the ATM switching equipment on the transmission side can readily set the alternate SVC by making reference to the management table.
According to fourth solving means, in the above-mentioned first solving means, for the purpose of detecting any of failures, the physical states of line interfaces from the adjacent ATM switching equipment are monitored, and the line failures are detected on the basis of the light reception loss, the pull out and the like. The SVC is established with such concrete and physical failure detection as a turning point, whereby it is possible to cope very speedily with the failures.